U.S. Pat. No. 5,648,454 (to GE) discloses synthesis of co-polyesters from co-cyclic compositions. This patent does not disclose polymerization in the presence of linear polymer.
EP 0 655 476 A1 (to GE) discloses polymerization of polyester cyclic oligomers specifying that the cyclic oligomers be free of linear polyester at the beginning of polymerization.
Modification of a premanufactured linear polyester by copolymerization with a polyester cyclic oligomer of different chemical composition with the intent of preparing polyesters of lower ultimate crystallinity is described in Cook, T. D.; Evans, T. L.; McAlea, K. P.; Pearce, E. J., U.S. Pat. No. 5,300,590 (1994) to GE.
JP 47-6425 (to Nippon Ester) discloses a means of post-polymerization molecular weight enhancement of linear polyester by adding cyclic oligomer to a melt of linear polyester. In this process, the linear polyester is made by conventional means and the cyclic simply provides on-line molecular weight enhancement. Our invention provides an entirely new method of making polyester.
There are many references on cyclic oligomer polymerization. However, none of these references teach the benefits of cyclic polymerization in the presence of linear polyesters which overcomes the high melting points of the cyclic oligomers, a difficulty often associated with cyclic oligomer polymerization.